Wednesday, April 5, 2017

Behind Your Bony Mask of Face

We all know what this post is about.

Below I will present a few small screen grabs cut out of larger pics of skulls. Let's just say that the representative animals are quite diverse phylogenetically. But despite the disparate vertebrae groups there are some striking similarities - and differences - in the bony texture. Before I reveal what animals are represented I would like readers to simply focus on the textures and patterns at hand, without any phylogenetic prejudices in mind.One of these things is not like the other…

A.

B.

C.

D.

E.

F.

G.

H.

I.

J.

K.

Again, without any phylogeneticprejudices creeping into your decision making, what similarities and differences do you observe? Which examples are more textured, which are less? There is a story to tell in all of this I will suggest and after the players are revealed I am going to offer that it is more behavioral - more adaptationist (there is that dirty word again) - than strictly phylogenetic..........A. Belongs to a stinkin' fur ball, the lowland Paca. Amazing is it not? These zygmotatic plates have something to do with the sound propagation of this cheeky little guy. Not only is this animal a bit of an outlier for its mammalian pedigree but it is also an outlier for its terrestrial inclinations.

I. Daspletosaurus horneri. Does it really compare that favorably to the other examples? I'm not seeing it. There is a general rugose nature to it, but hardly as intricate bone texture as the other examples…

Did I hit you over the head enough with rugose skulled swamp monsters?

The recent paper on the Two Medicine Formation tyrannosaur and associated facial integument inferences (Carr et al., 2017) makes the case that crocodile facial integument is the best inference for tyrannosaur facial integument. Also worth mentioning is that this is the argument that Tracy L. Ford (Ford, 2015) has long been making for quite some time (though Carr et al. did not deem fit to mention him). While the media has certainly ran with the story, at least in the online paleo community reaction to this inference has been highly skeptical. I don't want to recount the variable criticisms to Carr et al's inferences as many have done that already. However what should not be lost on our observations is that several of these textured skulls above come from animals that do not have tightly adhering skin texture such as the various amphibians. Or even have scales at all.

There is potentially a story to tell here...

Let me make another analogy to fantasy creatures. For me one of the most entertaining aspects of fantasy creature creation is to unpack the various - and often times disparate - elements from contemporary or extinct creatures that are spliced together to create a fictional animal. For me one of the most successful creature splices of recent years is the Bashee and Great leonopteryx from Avatar. Darren Naish does an excellent unpacking of the various inspirations and spliced bits of microraptor, bird, pterosaur, bat, fish, and sports car design that went into the creation of these animals.

It is the liberty in splicing all of these disparate animals together that creature creators do to make a strange but believable fictional animal that paleontology needs to take more inspiration from.

I think the Carr paper is valuable because it draws attention to crocodile skull texture. Yes it is true that tyrannosaurid skulls show some gross similarity to crocodile skulls in sharing a rugose texture and if you had to draw a rough comparison as to what animal best matches large tyrannosaur skull texture crocs are a good analogy. But crocs evince this rugosity all over the skull, tyrannosaurids have many smooth parts with the rugose sections being localized across more of the rostral sections. Of the animals presented above I would posit the Daspletosaurus skull as being the most different texturally from the others. People are naturally drawn to to comparing tyrannosaurids to crocodiles because they are related and predatory. However most theropods (except spinosaurids) are quite distinct from crocodiles ecologically. And that is the gist of what I am suggesting, we are potentially witnessing bone texture as an ecological signal - not as a phylogenetic/anatomical one. Instead of asking; what other archosaur skull looks most like a tyrannosaur skull? we should be asking; why does a crocodile skull look so similar texturally to a temnospondyl, catfish, snapping turle etc etc. skull?

When we see a diverse array of animals exhibit a remarkable similarity in facial bone texture as well as a remarkable congruence of ecological niche - ambush predator of murky, aquatic haunts - we have to seriously question if this bone texture is really a phylogenetic-anatomical message or an ecological one. There is more than a reasonable and persistent trend of highly pitted, rugose, and textured skulls among aquatic and amphibious stealth/ambush predators. The question is why?

My hypothesis is that such skulls in aquatic predators - highly textured with increased surface area but still maintaining streamlining - work as enhanced sound/vibrational interceptors. Like an old, well used catching mit these rugose skulls are better able to intercept, transmit, and "grab" acoustical/vibrational frequencies in a visually limiting aquatic environment. Vibration may travel through tissues in different ways and bone might offer an added layer of frequency interception that - when combined with other tactile organs (nerve endings, pressure domes, "whiskers" etc. etc. ) allows for a more comprehensive reading of the environment.

So why do tyrannosaurs - and many theropods - have such rugose skulls? Well in the case of spinosaurids (and maybe other theropods that exploited aquatic environments predominantly) it is possible they converged on a highly textured design for the same reason that other aquatic predators potentially did - it enhanced sensitivity. For most other other theropod skulls - including tyrannosaurids - I would like to advance an argument from material science: that there is a relationship between bonding strength and surface roughness. In this case the two materials are skin and bone and a rugose bone texture allows for skin to better anchor on the skull - growing into all of the nooks and crannies with increased surface area - in light of a particularly traumatic bite prone existence. That this bone texture is most prominent on the parts of the "snout" most devoid of overlaying musculature and exposed to bites we should expect this rugose nature to be most prominent there. Which it is. Unlike a crocodile skull which displays rugose formations across almost all of the skull - in line with the potential use of such rugose formations to discern water borne vibrations.

There is potential analogy to the textured skull of theropods acting as a structural adhesive to skin argument: hippo skulls. Animals which have tremendous lips and a very battle prone, bite weary existence. They don't have smooth bone where the lips and skin anchor - they have textured, rugose bone .

credit stock vault author Bjorgvin Gudmundsson

And for the record I do agree with Carr et al. (and Tracy L. Ford btw) that tyrannosaurids (& other theropods) did have exquisitely sensitive, tactile faces. But it was through large lips that grew out from the neurovascular foramina that these nerve endings felt and sensed their world - both the real time struggles of their prey and the touch of a mate or hatchling. It is patently obvious that the pattern of foramina on the dentary (bottom jaw) are arranged in such a way that the upper teeth will not cut into the labial tissue that grows out from them. Note that this is not the pattern we see the foramina take in the crocodile dentary - where they emerge right up next to the teeth.

I also agree that they were probably more romantic and tender than we might typically imagine.

Ford, T. L., 2015, Tactile faced Theropods: Journal of Vertebrate Paleontology, SVP 75th annual meeting, Meeting Program & Abstracts, p. 125."A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

18 comments:

Alessio
said...

Yeah, as soon as i found and read the paper (and also gazed upon the life restoration in the aforementioned paper... Ugh!), my opinion on theropod head gears, well, hasn't changed as much as the media coverage about this paper promised.The classic problems regarding the comparision between rexes and crocs are still there, there's nothing truly groundbreaking (say, a preserved Daspletosaurus "mummy" or something like that) and while i liked the paper for some reasons (the anagenesis stuff is actually pretty interesting, for example), for another part i tend to consider it just another well-presented theory about dinosaur integument. Nohing less, nothing more.

Great post Duane. I had the same general assumption that those weird facial grooves were used for sensitive "feeling about", either by anchoring nerves, whiskers or something else. I especially found this common in aquatic animals, so I'm glad to see my assumption come true.

On the matter of Daspletosaurus' exact facial integument, are scales still likely from this paper's evidence? And even if it's not assumed from the paper, could it still be a likely trait?

As many have pointed out the paper's contention that Daspletosaurus (and by extension other tyrannosaurids) were both croc-like and scaled is troubling for the mere fact that crocs are not scaled on the head. Someone on the authorship or in peer review should have stipulated this point or corrected it. I don't particularly lean towards scales on the head because if we assume a Yutyrannus like ancestor that went complete with a filamentous integument and then lost part or most of it on the head and neck I would hedge my bets towards what we see in birds that lost feathering on the head: nekkid skin. Now I can't rule out scales as of yet but I don't find any overwhelming evidence for scales on the head. It is also weird that some have read the headlines and interpreted this paper as having solid evidence i.e. preserved facial integument for scales.

To clarify:do what you want; scale it; feather it; fleshy tufts of thick skin; keratinize it. At this stage in the game I am not particularly vocal about limiting integumentary structures on tyrannosaurids as there is little much but educated guesses IMO. With the exception that you don't put a beak on it. We should have fun with the freedom at this stage in the game. Unfortunately this freedom comes with a price and that is internet know it alls that want to ruin all of the fun!!

Yeah, I think the biggest disservice the paper made was to call the skin on the snout "scales". Especially considering the croc-crack paper concluded that the scales aren't literally scales. Ironically the skull found to be most similar in the study was Alligator mississippiensis which doesn't have the cracked skin on the snout. Even if we entertain the possibility that Tyrannosaurs and Crocodilians had exactly the same bone structure in the snouts it would still be a misnomer to say the snout was "scaled". In fact, if they left it at "the face of tyrannosaurs was most similar to crocodilians" it would have made more sense, rather than saying explicitly that they looked exactly like a crocodile. I often wonder what birds would look like with fully developed maxillae with teeth, would they resemble their nan-avian descendants? Not that I am advocating in any direction myself, I don't care one way or the other. I just don't think it is very helpful to imply a possibility as something known when we don't know for sure.

@Nick Indeed. Croc like facial skin is a good idea worth exploring and indeed I think it likely in theropods that converged ecologically with crocodiles. For now I think assuming a lipped ancestral condition >that could become lipless under certain circumstances< is a useful place to start. There is a good potential explanation for why bird line theropods lost lips and evolved beaks and why piscivorous theropods lost lips: I'm not seeing an explanation for why tyrannosaurids and other meatosaurs lost their lips...

Yeah, I mean unfortunately I see these oversights a lot. The problem IMO is the nature and outdated methodology of modern scientific publishing. Most papers have but two unpaid reviewers. Imagine if the process could harness the power of the internet in a sort of "group sourcing of review" where a form of pre-print is made available for public input and review. Where everyone from informed enthusiasts to vouchered Phd's could chip in. IMO opinion it makes for a more exciting, engaging, transparent, and collaborative process. Unfortunately scientific publication has a business model, career scientists are competitive and want their names first authorship, and teh ego ruins everything.

Maybe I am a naive dreamer but I see a better way for scientific communication to be enacted which combines the accessibility and immediacy of blogging with the legit peer review (not just by 2 but by many) of academic literature.

Such a format would also allow people whose work is relevant but which was disregarded a voice.

Well, I do not think you analyzed it properly. We can see it in the very beggining: you put many skulls of different creatures there and says that just because all of them have rugose skull texture the comparation with crocodiles is not a great one, however you simply forgot that, even tough rugose texture can be caused by many things, it is obvious that different causes will lead to different irregular textures on the skull (muscle attachment changes the surface of the bone, but the marke are clearely not the same as those of crocodylian keratinized skin). Therefore your first point does not stand.

You said that people like to compare T. rex with crocs because they are predatory, but this is simply not the case. We are talking about fossil data and accuracy, not a simple fan made comparation to make T. rex look cool (I did not want to be rude in this part. Just explaining).

And if the iregular texture of T. rex's skull was due to bites from rivals, the paleontologists would have realized it. The teeth have a specific shape and thanks to this it is easy for an authority in the subject to identify tooth marks left by a rival of it's own kind (that is how it was Discovered that Sue had a parasyte on her jaws when it died), but the texture found resembled that of a crocodylian skull. All of this without mentioning that:

- It was shown that the irregular surface goes almost all the way to the tooth row. It is nearly impossible for a T. rex to have had such an enormous area of it's snout bitten like that (just have the shape of the jaws in mind);

- D. horneri, just like D. torosus, had thin teeth designed for slashing and cutting. Such jaws would have NEVER left marks like those seen in T. rex.

Duane didn't say that the irregular texture was CAUSED by bites, but rather postulated that it was an adaptation to allow the skin to adhere more strongly to the skull as a defense AGAINST bites. He also said nothing about muscle attachments, either. He's always made a strong argument that theropods would've had little to no facial musculature.

Douche-baghakin I have already blocked you on deviant art, yet you seek me out on multiple social media formats; Facebook; google+; my blog you corrupt with your toxic attitude and thought process. I have been ignoring you in the hope that you will do the same to me as I have done to you and just ignore me. Just leave me alone. Don't pester me on Facebook, on my blog, or on google+. I know of what slanderous and dishonest things you perpetuate about me on your own very boring deviantart page. Seriously why are you even on deviantart it is for creators - not bloviators like yourself - as you are a world class bloviator. That's all you do is bloviate, on and on. You don't bring any value, beauty, or originality to the world. I will not now, or in the future respond or comment on anything you post. Got it nimrod? You have lost the privilege to communicate with me. I don't consider you a peer; a competitor; a colleague; or even an informed enthusiast. You have lost a forum with me. I am not paid to do this - nor do I need to waste my energy, time, and emotion on a toxic loaf of monkey spunk like yourself.

Remember it is you that are seeking ME OUT not the other way around. GO to some other dungeon of the internet and just stop - let's call it what it is - harassing me. If I have not made it clear enough through me blocking you on deviant art that I want NO part of you let me spell it out. LEAVE ME ALONE. If I am so wrong in any of my ideas or arguments it will be others much smarter and more informed than you to point out my errors not a bloviating, petulant knuckle-head like you.

Got it pest? Fuck off. Any future comments from you will be quickly and judiciously deleted. I owe you nothing. I don't owe you a forum, a dialogue, an open debate. You are a pig that likes to roll around in the mud and I will not get dirty with you.

FUCK OFF.

Any future requests or pleadings for communication from you to me I will treat and document as harassment. Cuz it is you seeking me out - not the other way around.

Hey Duane, first time poster! Would you mind pointing me to paleontologists' opinions on the Carr et all paper? Both you and RJ Palmer have mentioned the paleontology community has been somewhat skeptical about the Carr paper but I haven't been able to find the responses (note this is not to undercut what you and RJ are saying, I trust both of your judgments but I'd like to see what the responses say since neither of you specified what problems there were with the paper). I'd really appreciate it, thanks!

Btw. sorry if I've triple posted this, the website is not providing me with feedback if I've actually posted or not.

I am not going to speak on behalf on any professional paleontologists as I don't want to misquote or paraphrase incorrectly but surveying a wide swath of opinion on social media gave me the impression that - at many levels - opinion on the new species/phylogeny aspect was generally solid. However on the soft tissue inferences opinion was - at many levels - decidedly less solid. The great thing about today is that anyone who want to put the time in can cultivate and follow a range of thinkers on this subject on fb/twitter etc. etc. and that is what I would advise you to do Jeffrey. I don't want to quote someone from a Facebook or twitter response, but I'm sure if you did some sleuthing you would find the general thrust of thinking as such: that the new species/anagenesis argument seems pretty good but the soft tissue inference is lacking.

As I touched upon in this post the pattern of skull texture in crocodilians may actually have more an ecological signal than a soft tissue signal (no one is suggesting that temnospondyls have a tight fitting scaled head integument). Additionally the authors made some very simple mistakes in their choice of language in the soft tissue inference. Crocodiles do not have scales on their head:http://ot-ds.sipr.ucl.ac.be/cps/ucl/doc/bdiv/documents/1_-_Science_2013.pdf

I don't know what RJ Palmer said can you link to something?

As far as "consensus opinion" goes I myself don't lean on it too much. Maybe you are new to the blog or my thoughts but even a cursory investigation on my thoughts should reveal as much. However in this case I do converge with - at least what I interpret from social media cues - as a general sentiment that the soft tissue inference is lacking. Again consensus is not really the selling point of this piece or what has now or has historically dictated my personal thinking on matters. While taking a subjective purview of social media sentiments is not the ideal situation - it is perhaps what we have now at this time to make a best time capsule of thought. If you want what someone thinks on the record I would go them personally.

Interestingly I do think a number of theropods did have croc-like, nonscaled tactile faces ( an idea that Tracy L. Ford should get credit for btw not Carr et al.). Spinosaurids, maybe some coelophysids, unenlagines including spinosaur mimics like Austroraptor. I will delve more deeply into croc-like facial integument for theropods in the future btw.

"Sorry if I've triple posted this" That's ok i have my comments on moderation because there is a lurking, harassing character that keeps spamming me and for the time being I have to moderate. I hate it too.

RJ mentions his stance on his most recent post on Deviant Art: http://arvalis.deviantart.com/art/Naked-Boy-Stan-673707322

I get the moderation stuff. I saw your response to Dovakiin. That person always has something rude and controversial to say whenever he posts. Good on you to put your foot down. I do wonder if they're a troll or if they actually believe what they say.

Are there any paleontologists you would recommend following on social media?

I look at a wide swath of people's opinion. Just start exploring and visiting people to see whom is connected to whom and it is not to hard to follow people depending on what expertise your interest falls into, Cheers

The hippo skull's rugose surface is interesting, and certainly a good example refuting Tracy Ford's poster. What anchors to that part? Facial muscle most likely. Than why doesn't most mammals(except for elephant seal) have such rugose texture?

@Yunwoo Lee For the hippo rugosity I can't speak with certainty - and I've never dissected a hippo - but in that area where the rugosity occurs the main muscle is the lip muscle, orbicularis oris, and it does not connect to bone usually in mammals but is sort of free floating in the face. Interesnngly I have come across another group of big headed archosaurs that most certainly did not have scaled faces but do have very rugose skulls which I will discuss in a future post.